This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. ABSTRACT Vitamin D deficiency is widespread and linked to decreased bone mineral content. Little data exists regarding the vitamin D status and the relationship of 25-OHD status to functional bone health outcomes in Hispanic infants. To evaluate this, we plan an observational cohort of full term, healthy, exclusively breastfed Hispanic and Caucasian infants. We hypothesize serum 25-OHD measured in cord blood will be significantly lower in Hispanic than Caucasian infants, with 25-OHD 50% of Hispanic neonates. Hypothesis #2: Speed of sound bone ultrasound (SOS U/S) and dual-energy X-ray absorptiometry (DXA) whole body bone mineral content measured in the first week of life will correlate positively with 25-OHD concentration in cord blood. Hypothesis #3: Supplementation with 400 IU/d of vitamin D3 from birth will allow all infants to achieve 25-OHD levels 20 ng/mL. Baseline-adjusted bone mineral content and SOS U/S will be significantly correlated with 25-OHD status at 3 months. II. SPECIFIC AIMS Primary Aim: To evaluate the relative frequency of vitamin D deficiency in human milk fed Hispanic compared to Caucasian newborn infants in Houston, Texas. Secondary Aims: To determine if infant vitamin D status is related to bone mineral status at birth and to determine the effects of vitamin D supplementation on 25-hydroxyvitamin D (25-OHD) concentration and bone mineral status vitamin D deficient and vitamin D replete infants at 3 months of age. III. BACKGROUND AND SIGNIFICANCE In recent years, severe vitamin D deficiency has resurfaced as a major public health concern. Nutritional rickets is widespread, and a recent report on this disease in Texas showed Hispanic children are at increased risk. Long-term follow-up has demonstrated that vitamin D deficient infants are more likely to have decreased bone mineral status in late childhood. Additionally, vitamin D deficiency has been linked to changes in fetal imprinting and increased susceptibility to autoimmune diseases, immune deficiency, and malignancy. At birth, an infants vitamin D status is entirely dependent on the vitamin D status of the mother. Many studies have shown vitamin D deficiency is very common in mother-child pairs, especially in dark-skinned individuals. However, few data exist regarding the vitamin D status in Hispanic infants. Low milk intakes and decreased sun exposure with urbanization makes this a very high-risk group among infants in Texas.